1. Field
This invention relates generally to compositions which include liposome vesicles which entrap substances therein. More specifically, this invention relates to compositions for topical application which comprise liposome-entrapped substances providing bacteriostatic and antibacterial action.
2. State of the Art
In recent years there has been an increase in development of liposomes for use as "containers" for substances which are liberated under specific conditions. Liposomes are small, closed vesicles formed from lipids, particularly phospholipids. Lipids generally have a hydrophobic end or "tail" and a hydrophilic end or "head." When mixed with water, the hydrophobic ends join together toward a common center while the hydrophilic ends become oriented outwardly to interface with the water. More than one layer of lipids, known as a bilayer, forms a liposome having an inner space and an outer surface. Liposomes may have more than one bilayer.
Compositions which include substances encapsulated within the inner space of the liposome have been used in different applications. For example, in U.S. Pat. No. 4,957,735 to Huang dated Sep. 18, 1990, liposomes are used to entrap antibodies for site-specific delivery to disease affected cells within a body. U.S. Pat. No. 4,766,046 to Abra, et al., dated Aug. 23, 1988 discloses the use of liposomes to bind antifungal agents for injection into a body. Bound liposomes are also used in immunoassay procedures as disclosed in U.S. Pat. No. 4,783,400 to Canova-Davis, et al., dated Nov. 8, 1988, and in U.S. Pat. No. 4,874,710 to Piran dated Oct. 17, 1989.
Liposomes have been modified in various ways to provide particular desired properties, such as time-release and site-specific release. Examples of such modifications are disclosed in U.S. Pat. No. 4,921,757 to Wheatley, et al., dated May 1, 1990 (disclosing methods of making liposomes to respond to a specific stimuli, such as pH or temperature); U.S. Pat. No. 4,766,046 to Abra et al., cited previously, (disclosing formation of liposomes having a particular size); and U.S. Pat. No. 4,708,861 to Popescu, et al., dated Nov. 24, 1987 (disclosing the sequestration of liposomes containing bioactive ingredients in a gel matrix to control release of the bioactive ingredient following injection into a body). The preparation of liposomes is generally discussed in U.S. Pat. No. 4,830,858 to Payne, et al., dated May 16, 1989, the contents of which, specifically at col. 1, line 17 through col. 8, line 4, are incorporated herein by reference. Payne is specifically directed to a spray-dry method for preparing stable liposome precursors.
To date, liposome technology has been directed mainly to use as a carrier for substances, such as drugs, to be injected into a living body. Liposome technology has also been directed to use as a carrier in assay or immunoassay procedures. A detailed discussion of liposomes as carriers is set forth by Ryman, B. E. in "The Use of Liposomes as Carriers of Drugs and Other Cell-Modifying Molecules," Proc. 6th of the Int'l Congr. Pharmacol. 5, 91, published in "Drug Applications," Clinical Pharmacology, vol. 5, pp. 91-103, Pergamon Press (1975).